The present invention relates to a radio unit with a security function against robbery and, more particularly, to the radio unit with a function to display information regarding an illegal access from an external terminal.
Conventionally, using a Read Only Memory (referred to as ROM, hereinafter) writer and the like it is possible to change information, such as a call number, stored in the radio unit from the external terminal. First an access password is input to the radio unit from the ROM writer and the like. The password should match with a password stored in the radio unit. Only when the passwords match each other can individual information, such as the call number, be changed. This prevents information of a stolen radio unit from being changed.
A radio unit in the prior art for preventing an illegal access is disclosed in Japanese Patent Laid Open No. 48519 (1993). In this prior art, a data control unit checks a radio unit password stored in a memory of the control section with a password stored in a ROM for an individual selection number of the individual selection call receiver. When the check result indicates mismatching, the ROM for the individual selection number cannot be read/written.
Another prior art apparatus for preventing an illegal access is disclosed in Japanese Patent Laid Open No. 240930 (1992). In this prior art, an input password and a password stored in a receiving unit are compared and acceptance of the password is stopped if the number of occurrences of password mismatching exceeds a preset value.
Changing individual information, such as a call number, is primarily changed by an authorized user, radio system operator or its agent. The authorized user may make a password input error once or a few times.
However, according to the prior art disclosed in Japanese Patent Laid Open No. 48519(1993), the ROM for individual selection number cannot be read/written after a password mismatch occurs.
Similarly, in the prior art disclosed in Japanese Patent Laid Open No. 240930 (1992), the ROM for individual selection number cannot be read/written if an incorrect password is entered a predetermined number of times.
Also, in Japanese Patent Laid Open No. 240930(1992), the apparatus allows access to individual information and automatically deletes password input error history when password matching is detected within a predetermined number of times even if password mismatching has previously occurred.
In these conventional devices, however, it is not possible to ascertain that the radio unit, of which individual information was rewritten by a robber, is a stolen one.